1. Field of the Invention
The invention relates to compositions composed of polyvinyl acetate and vinyl acetate-vinyl laurate copolymer, to processes for their production and to their use in chewing gum base.
2. Background Art
Typically, chewing gum formulations are composed of a water-insoluble chewing gum base and a water-soluble fraction, the latter comprising sweeteners and flavorings which are leached out by the saliva during chewing.
In general, in the production of chewing gum base, in addition to solid elastomers, for example polyisobutylene, isobutylene/isoprene copolymers and/or butadiene/styrene copolymers, a vinyl acetate homopolymer is used as a polymer resin. Suitable elastomer solvents are, for example, polyterpenes or glyceryl esters of rosin or partially hydrogenated rosin. The plasticizers used are frequently hydrogenated vegetable oils, cocoa butter, paraffin waxes, natural waxes and polyethylene. Additional plasticization is achieved by the use of triacetin, and/or emulsifiers such as glyceryl monostearate, acetylated monoglycerides of natural fatty acids and/or lecithin.
The chewing gum bases can be produced in one or more stages. Typically, in a batchwise process, mixers or double-Z kneaders with high shear force are used for this purpose. Alternatively, EP 0763328 describes continuous processes in which the chewing gum base is produced in an extruder.
U.S. Pat. No. 4,968,511 recommends using, as the chewing gum base, one or more polymers such as homopolymers of vinyl esters of carboxylic acids having from 3 to 10 carbon atoms, copolymers of two different vinyl esters, copolymers of vinyl ester and ethylene, and the terpolymers of vinyl alcohol, vinyl ester and ethylene. To produce the gum base, the individual constituents of the formulation, such as polymer resin, elastomer, filler and emulsifier, are metered successively into a preheated mixer.
U.S. Pat. No. 5,173,317 discloses the use of vinyl acetate-vinyl laurate copolymers instead of polyvinyl acetate as the gum base. Owing to the elastomeric properties of vinyl acetate-vinyl laurate copolymers, it is possible to dispense with the use of further elastomers in the formulation. Here too, the individual constituents of the formulation are metered successively into a preheated mixer and mixed in the melt.
A disadvantage in the case of use of vinyl acetate-vinyl laurate copolymers is that they are obtained as tough, elastic blocks which cannot be used directly in the customary processes for producing chewing gum mixtures in batch kneaders or extruders. The blocks have to be comminuted beforehand, which is possible only with a high level of cost and inconvenience owing to the tough, elastic material, for example by freezing the material and subsequent comminution. A further means of converting the vinyl acetate-vinyl laurate copolymers to a ready-to-process form is to melt them and to meter them into the kneader or extruder as a melt.